1. Field of the Invention
The present invention relates to a light-receiving detection device which consists of a holder for holding an optical system and a light-receiving sensor. More specifically, the present invention relates to the contact positions of said holder and said light-receiving sensor.
2. Related Background Art
Conventionally, after a holder is placed around the light-receiving surface of a light-receiving sensor and its position is adjusted, these two components are assembled into a sub-assembly by applying a quantified amount of adhesive from a dispenser. In this case, a dribble surface is formed in each side of the holder. The adhesive applied on the dribble surface dribbles downward to the boundary of the dribble surface and the contact surface of the light-receiving sensor, which is visually checked.
FIG. 7A is a perspective view in which the holder 1 is placed around the light-receiving surface 2b of the light-receiving sensor 2. And FIG. 7B is an enlarged perspective view showing the contact area of the light-receiving sensor 2 and the holder 1 shown in FIG. 7A. The holder 1 has an upper opening and a lower opening, and an optical path penetrates the holder between these openings. An image-forming optical system (not shown) is held in the optical path.
As shown in FIG. 7B, the dribble surface 1a is formed in the side of the holder 1. FIG. 8 shows the holder 1 and a nozzle discharging the adhesive 3a toward the dribble surface 1a of the holder 1. The light-receiving sensor 2 which is used to detect a focal point is bonded to the holder at two positions. But, for brevity, only one of the two contact areas will be described. As shown in FIG. 7B, the bottom of the holder 1 is brought into contact with the contact surface 2a of the light-receiving sensor 2. And the position of the holder 1 is adjusted. Then, as shown in FIG. 8, the tip 3b of the nozzle 3 is set near the contact surface 2a of the light-receiving sensor 2 to discharge the adhesive 3a from the tip 3b.
The adhesive 3a discharged onto the dribble surface 1a gradually dribbles downward to the boundary between the bottom of the holder 1 and the contact surface 2a of the light-receiving sensor 2, and cures there to bond the holder 1 to the light-receiving sensor 2.
The dribble surface 1a is surrounded by side walls 1c and 1d (see FIG. 7B) and an upside wall 1b (see FIG. 8). These walls prevent the adhesive 3a applied onto the dribble surface 1a from spreading from the dribble surface la, and lead the adhesive 3a toward the boundary of the dribble surface 1a and the contact surface 2a of the light-receiving sensor 2.
The behaviour of the adhesive 3a in the vicinity of the boundary will be described with reference to FIG. 11. If adhesive is applied over the boundary C of a vertical surface A and a horizontal surface B, the adhesive is to spread along the boundary C. According to the same principle, the adhesive 3a which is applied onto the dribble surface 1a as shown in FIG. 8 and which dribbles downward to the boundary of the dribble surface 1a and the contact surface 2a spreads along the boundary without spreading over the contact surface 2a. Then, the adhesive which has spread along the boundary cures to bond the holder 1 to the light-receiving sensor 2.
As shown in FIG. 8, however, since the lower part of the tip 3b of the nozzle 3 is set close to the contact surface 2a, the nozzle 3 can easily touch the contact surface 2a. If the tip 3b of the nozzle 3 touches the contact surface 2a while set close to it before the adhesive 3a is discharged, the holder 1 may shift on the contact surface 2a and the subassembly may become a defective.
In order to solve this problem, the tip 3b of the nozzle 3 can be set near the upside wall 1b, as shown in FIG. 9. In this case, however, the adhesive 3a discharged from the tip 3b of the nozzle 3 onto the dribble surface 1a is attracted through and up above the upper part 3c of the tip of the nozzle 3 and the upside wall 1b of the holder 1b; the capillary phenomenon. Once some of the adhesive 3a stays in the cavity between the upside wall 1b and the dribble surface 1a, it attracts the newly discharged adhesive 3a toward the upside wall 1b.
Even when the tip 3b of the nozzle 3 is set closer to the dribble surface 1a as shown in FIG. 10, the adhesive 3b discharged from the tip 3b of the nozzle 3 is also attracted upward according to the capillary phenomenon caused by the upper part 3c of the tip of the nozzle 3 and the upside wall 1b. And also in this case, when a certain amount of the adhesive is discharged, the adhesive 3b on the dribble surface 1a which is attracted upward comes in contact with the upside wall 1b, which attracts the newly discharged adhesive 3a toward the upside wall 1b.
The more adhesive 3a spreads over the upside wall 1b, the stronger the attraction becomes. Thus, the adhesive 3b can not reliably flow down toward the contact surface 2a of the light-receiving sensor 2.
As described above, according to the conventional art, it is very difficult to position the tip of the nozzle, and the holder can not be reliably bonded.
Further, in order to obtain the proper functions of the light-receiving detection device, the holder and the light-receiving sensor to be assembled have to be positioned with high precision. And since the device should work properly in various environments (such as high- or low-temperature, high humidity, or the like), the contact areas of the light-receiving sensor and the holder should be strongly bonded.
Now, a conventional light-receiving detection device will be described with reference to FIGS. 16 to 19.
FIG. 16 is a perspective view of the light-receiving sensor 2 and the holder 1, in which the holder 1 is set around the light-receiving surface 2b of the light-receiving sensor 2. FIG. 17 is an enlarged perspective view showing the contact area of the light-receiving sensor 2 and the holder 1 shown in FIG. 16. The holder 1 shown in FIG. 16 has the upper opening and the lower opening, and the optical path penetrates the holder between these openings. The image-forming optical system (not shown) is held in the optical path. As shown in FIG. 17, a ditch 1b of several tens of ms is formed on the contact surface 1a of the holder 1 which comes in contact with the contact surface 2a of the light-receiving sensor 2 so that the adhesive can spread between these contact surfaces 1a and 2a.
The adhesive 3a is applied along the contact portions of the contact surfaces 1a and 2a as shown in FIG. 18 so that it can flow into the ditch 1b shown in FIG. 17. And when the adhesive cures, the holder 1 is bonded to the light-receiving sensor 2.
As is shown in detail in FIG. 19, however, the ditch 1b is formed only in part of the contact surface 1a of the holder 1 and does not traverse the holder 1 from the side surface 1c to the opening portion. Accordingly, the adhesive 3a applied as shown in FIG. 18 can flow into the ditch 1b shown in FIG. 17 but often can not fill the entire ditch 1b because of the air remaining in the ditch 1b. As a result, the adhesive strength of the holder 1 to the light-receiving sensor 2 may vary. In order to prevent the dispersion in the adhesive property, the application of the adhesive 3a into the ditch 1b is now visually checked. But, it is often difficult to judge whether the adhesive 3a fills the entire ditch 1b shown in FIG. 17 or not from the outside.